Seim Lab Research

• SABSOON, SABLAM and SEACOOS
(Harvey Seim, Cisco Werner, Brian Blanton and John Bane)

The South Atlantic Bight Synoptic Offshore Observational Network (SABSOON) was initiated in 1998 as a government/academia partnership to develop ocean observatory capabilities off the Georgia coast (Seim, 2000). The focus of the program was to instrument Navy-owned platforms with oceanographic and meteorological sensors to provide real-time information of the coastal ocean state. The program is entering its sixth year and continues to expand. A number of multi-year datasets now document shelf conditions throughout the year, and are revealing the nature of seasonal and interannual variability and a range of processes on the shelf including internal tides, benthic resuspension events and coherent offshore transport events.

The South Atlantic Bight Limited Area Modeling program was a NOPP-funded follow-on program to the initial SABSOON program that sought to develop a coastal ocean nowcast/forecast system that utilized the real-time SABSOON observations through data assimilation. It has significantly advanced our understanding of the tidal dynamics in the South Atlantic Bight and begun to clarify the importance (Blanton et al, 2003) and variability of density field on the shelf.

The SEACOOS program is an ONR-funded effort to plan and serve as a pilot regional coastal ocean observing system (Seim et al., 2003). It involves the simultaneous development of observing, modeling, data management and outreach/education activities in a coordinated fashion to enable a real-time information system for a significant portion of the US coastal ocean. The SABSOON and SABLAM programs were precursors to the SEACOOS regional activity and allowed the program to ramp up quickly. SEACOOS has a broader extent and includes new observing capabilities along the NC coastline (e.g., Stearns et al., 2004) as well as off the east and west coasts of Florida. Funding is provided by ONR and NASA; collaborators include Nelson, Jahnke, (SABSOON); and Lynch, McGuillicuddy and Welsh (SABLAM).

• Offshore Buoy and Mooring System (Rick Luettich, H. Seim, students) (SEACOOS). As part of the SEACOOS program, Luettich is also collaborating with H. Seim to develop the Lookout Shoals Research Buoy. An uninstrumented buoy was deployed in early January off the Cape Lookout Shoals; this will soon be followed up with a fully instrumented buoy (Figure 3.35). The completed buoy system will consist of a bottom tripod containing a CTD and ADCP measuring mean currents through the water column and the surface wave field. The buoy will host a mid-depth and near surface CTD, and an extensive array of meteorological sensors. The buoy and bottom tripod will communicate via an acoustic modem and the buoy will communicate with shore via an Iridium satellite communications system and a cellular phone system.

Figure 3.35. Schematic of buoy/mooring deployed off Cape Lookout, NC.

• Autonomous Single Board Computer Acquisition System (Harvey Seim, SEACOOS) Seim has been developing a data acquisition system for use on offshore platforms (in particular, Navy towers associated with Tactical Aircrew Combat Training Systems, or TACTS) and on buoys. The system was originally conceived as a simplified, stand-alone version of the monitoring systems on the SABSOON towers, to be used on non-SABSOON platforms that lacked any supporting infrastructure (a number of the towers on the SABSOON range provide power and
microwave communications). The system uses a single board computer (SBC) as the main computational engine and addressable serial communications (RS485) to sensors wherever possible to enhance expandability. Solar cells provide power and Iridium is used for wireless transmission to shore [Figure 3.37: SBC-based instrument package (gray box) and one of the instrument staffs (anemo-meters not shown at SABSOON tower R4].

A full meteorological suite is hosted (short- and long-wave radiation, air temperature and humidity, barometric pressure, rain gauge, dual wind speed and direction) and can also accommodate an ADCP and multiple CTDs. A nearly unique aspect of the system is the use of a Windows CE operating system on the SBC and the use of a PPP connection, rather than zmodem or xmodem connection, for Iridium. The remarkably high bandwidth communications (in excess of 19200 baud) the system has achieved is suspected of being a result of the use of PPP and an ISP but, as yet, is not fully understood. Future deployments are planned for other offshore Navy ranges in the region (off NC and the FL Keys) but some technical and logistical issues must be resolved before these can occur.

• HF Radar on the Outer Banks of North Carolina (Harvey Seim) (SEACOOS). A CODAR Ocean Sensors Long Range high-frequency radar system was installed along the Outer Banks in late summer 2003 and has been operating more or less continuously since that time. Two antenna sets are deployed on the Outer Banks, one at the US Army Corps of Engineers Field Research Facility (FRF) in Duck (June, 2003), the other at the US Coast Guard Station at Buxton (August, 2003). Both sites have considerable man-made structures which complicate the deployments but provide needed power and communications infrastructure. The FRF site has been relatively problem free (except for communications problems) and the installation has required only occasional servicing (an antenna relocation following Hurricane Isabel in late 2003). The Buxton site has required regular maintenance as a result of initial permitting issues (with the National Park Service) and severe erosion at the site beginning in early summer 2004. Coverage has varied widely. The variability can be partly attributed to changing antenna locations, radio interference, and ocean conditions. Both sites, which operate at 4.5-5 MHz are affected by moderate to severe noise contamination. Recent software upgrades that enable new visualization tools, have allowed us to begin an investigation of this problem.

Despite these challenges we have been able to produce maps of ocean surface currents off the Outer Banks that include at least the landward edge of the Gulf Stream with some regularity. Initial quality assessments suggest the system captures the subtidal alongshelf flow field reasonably well but tends to under-predict cross-shelf currents. The spatial variation in tidal currents on the shelf is reasonably well captured and compares favorably with model predictions and previous field results. The tidal velocities are under estimated by 10-30%, and is possibly a function of the degree of temporal averaging employed in the processing. Alternative data processing algorithms are being developed.